Aromatic Hydrocarbons Aromatic hydrocarbons contain six-membered rings of carbon atoms with alternating single and double carbon-carbon bonds. The ring is sometimes shown with a circle in the center instead of the alternating lines. The term aromatic implies that compounds that contain a benzene ring have and this is true for many of them. These compounds are all around us. For example Cinnamaldehyde is responsible for the aroma of Methyl salicylate is responsible for the aroma of 21-11
Aromatic hydrocarbons are also the basis of many drugs, both legal and illegal. LP#7. Determine the molecular formula of each of the above compounds. The molecular formula should be listed in the order of C, H, N, O, S, halogen. Substitution Reactions of Aromatic Hydrocarbons Although benzene rings appear unsaturated, the double bonds DO NOT undergo addition reactions because they are so stable. A test for unsaturation will be negative! Instead, they typically undergo substitution reactions: where one attachment on the benzene ring is substituted with another. For example, H can be substituted for by Br: H can be substituted for by NO2: 21-12
Derivatives of Hydrocarbons A functional group is a reactive portion of a molecule that undergoes predictable reactions. All other organic compounds can be considered as derivatives of hydrocarbons. Organic Compounds Containing Oxygen Many of the important functional groups contain oxygen. Alcohols An alcohol is a compound obtained by substituting a hydoxyl group ( OH) for an H atom on a carbon atom of a hydrocarbon group. General formula: the OH is attached to a C with at most other C attached to it. e.g., methyl alcohol (aka methanol) or ethanol OR ethyl alcohol the OH is attached to a C with other C attached to it. e.g. 2-propanol OR isopropanol OR isopropyl alcohol the OH is attached to a C with other C attached to it. e.g. 2 methyl 2 propanol OR tertiary butyl alcohol OR t-butyl alcohol 21-13
Ethers An ether is a compound with an oxygen bridge between two alkyl groups. General formula: An example is: CH3 CH2 O CH2 CH2 CH3 CH3 CH2 O CH2 CH3 This is the most common ether, often called simply It can be used as an Aldehydes An aldehyde is a compound containing a carbonyl group with at least one H atom attached to it. General formula: A carbonyl group looks like: Examples are: ethanal a.k.a. acetaldehyde methanal a.k.a. Formaldehyde is used in the manufacture of plastics and resins. Formaldehyde is actually a gas, which is very soluble in water. An aqueous solution of 35% formaldehyde is sold as Formalin for use in disinfection and the preservation of biological specimens. Aldehydes can also be derived from aromatic hydrocarbons. 21-14
Ketones A ketone is a compound containing a carbonyl group with two hydrocarbon groups. General Formula: Examples are: dimethyl ketone 2-butanone Carboxylic Acids A carboxylic acid is a compound containing the carboxyl group, COOH. General Formula: An Example is: ethanoic acid The following table lists some common carboxylic acids 21-15
Esters An ester is a compound formed from a carboxylic acid, RCOOH, and an alcohol, R OH. General Formula for an ester: For example: ethanol acetic acid This is an example of a reaction. Organic Compounds Containing Nitrogen Amines Most organic bases are amines. Amines are compounds that are structurally derived by replacing one of the H atoms on ammonia with hydrocarbon groups. The general formulas are: These are all bases because the nitrogen atom has a lone pair of electrons with which to act as a Just like We can replace the ammonia with an amine. 21-16
Amides Amides are compounds derived from the reaction of ammonia, a primary, or a secondary amine with a carboxylic acid. General formulas are: primary amide secondary amide tertiary amide A sample formation reaction is: Also: ammonia acetic acid 21-17
Summary of Common Functional Groups 21-18